Antenna and dielectric substrate for antenna

ABSTRACT

This invention relates to a dual band antenna having a novel shape, which enables miniaturization and bandwidth widening. The antenna includes a dielectric substrate for an antenna including a layer of a planar element having a side edge portion constituted by either one of a curved line and line segments which are connected to each other while their inclinations are changed stepwise, and a substrate on which the dielectric substrate is placed and a ground pattern having a tapered shape with respect to the dielectric substrate is formed. The dielectric substrate and the ground pattern are juxtaposed, and a distance between the ground pattern and the side edge portion is continuously increased to become saturated as a point on the side edge portion moves away from a straight line passing through a feed position of the planar element. A resonant element is connected to the planar element at an end point of the planar element on the straight line passing through the feed position. By providing the resonant element, the dual band antenna can be realized. Besides, by the above structure, miniaturization of the antenna and bandwidth widening can be realized.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a wide bandwidth antenna, a dual bandantenna and a dielectric substrate used for those antennas.

BACKGROUND OF THE INVENTION

For example, a monopole antenna as shown in FIG. 16A is disclosed in“B-77: BROADBAND CHARACTERISTICS OF SEMI-CIRCULAR ANTENNA COMBINED WITHLINEAR ELEMENT”, Taisuke Ihara, Makoto Kijima and Koichi Tsunekawa, pp77General Convention of The Institute of Electronics, Information andCommunication Engineers, 1996 (hereinafter referred to as “non-patentdocument 1”). In FIG. 16A, a semicircular element 1010 is erectedvertically to a earth plate 1011, and the closest point of the arc ofthe element 1010 to the earth plate 1011 serves as a feed portion 1012.The non-patent document 1 discloses that a frequency f_(L) at which theradius of the circle corresponds approximately to a quarter wavelengthis the lower limit. Besides, it describes an example in which as shownin FIG. 16B, an element 1013 where a cut-out portion is provided for theelement 1010 shown in FIG. 16A is erected vertically to the earth plate1011, and that VSWR (Voltage Standing Wave Ratio) characteristics of themonopole antenna of FIG. 16A and the monopole antenna of FIG. 16B arealmost identical to each other. Further, it also discloses an example inwhich as shown in FIG. 16C, an element 1014 in which an element 1014 a,which resonates at a frequency lower than f_(L) and has a meandermonopole structure, is connected to an element with a cut-out portion asshown in FIG. 16B is erected vertically to the earth plate 1011.Incidentally, the element 1014 a is disposed to be accommodated in thecut-out portion. By the element 1014 a, the antenna also resonates at afrequency lower than f_(L), and multi-resonance is realized, however,the VSWR characteristic in a frequency range lower than f_(L) is poor,and sufficient characteristics for use in a dual band antenna are notachieved.

Besides, U.S. Pat. No. 6,515,626 discloses a microstrip patch antenna1100 as shown in FIG. 17. The microstrip patch antenna 1100 is such thata ground plane 1140, a microstrip patch 1120, and a triangular pad (feedconductor) 1130 connected to the microstrip patch 1120 are formed ofconductive metal on a dielectric substrate 1110. Incidentally, themicrostrip patch 1120 is fed from a feed point 1150 through thetriangular pad 1130 as a feed conductor. Although not shown, from theoperation principle of the microstrip antenna, the microstrip patchantenna 1100 as shown in FIG. 17 is not suitably operated unless theground is disposed opposite to the dielectric substrate 1110. Besides,since the area of the ground plane 1140 is very small, it is notconceivable that the ground plane functions as a radiant element.Further, in the microstrip antenna, a current flowing in the radiationconductor is not a direct radiation source, and in FIG. 17, a currentflowing in the triangular pad 1130 and the microstrip patch 1120 doesnot serve as a direct radiation source. Besides, a reception frequencybandwidth of the microstrip patch antenna 1100 disclosed in thispublication is as narrow as 200 MHz with respect to the center frequencyof 1.8 GHz, the triangular pad 1130 does not function as the radiationconductor, and it is conceivable that the microstrip patch 1120 is aradiation conductor of a single frequency (1.8 GHz). As stated above,the microstrip patch antenna 1100 shown in FIG. 17 is a microstripantenna and is not a monopole antenna in which a current flowing in theradiation conductor contributes to radiation. Besides, it is not atraveling-wave antenna in which the wide bandwidth is realized bycontinuously changing a current path flowing in a radiation conductor.Further, since the reception frequency range is single, it is not a dualband antenna.

As stated above, although there are various antennas up to now, sincethe conductor in the conventional monopole antenna disclosed in thenon-patent document 1 is erected vertically to the earth plate, the sizeof the antenna becomes large.

Besides, in the antenna disclosed in the non-patent document 1, as setforth above, although multi-resonance is realized in plural frequencyranges, antenna characteristics that are presently demanded as the dualband antenna are not obtained.

Further, with respect to the microstrip antenna disclosed in U.S. Pat.No. 6,515,626, although the shape appears to be such that both thetriangular pad and the microstrip patch contribute to radiation, thetriangular pad does not serve as the radiation conductor, but is merelythe feed conductor. Thus, this antenna is the antenna in which thereception frequency range is single, and is not the dual band antenna.

SUMMARY OF THE INVENTION

In view of the foregoing problems, an object of this invention is toprovide an antenna having a novel shape, which enables miniaturizationand bandwidth widening, and a dielectric substrate for the antenna.

Besides, another object of this invention is to provide a dual bandantenna having a novel shape, which enables miniaturization and hassufficient antenna characteristics, and a dielectric substrate for thedual band antenna.

An antenna according to a first aspect of this invention includes aplanar element that is fed at a feed position, and a ground pattern thatis juxtaposed with the planar element, and wherein as being farther awayfrom a straight line passing through the feed position, a distancebetween the planar element and the ground pattern is gradually increasedto become saturated. By juxtaposing the ground pattern with the planarelement, miniaturization of the antenna becomes possible.

Besides, a side edge portion of the planar element may be constituted byeither one of a curved line and line segments which are connected whiletheir inclinations are changed stepwise, and the planar element may beformed on or inside a dielectric substrate for an antenna.

When the planar element is formed on or inside the dielectric substratefor the antenna, further miniaturization of the antenna becomespossible. However, when the planar element is formed on or inside thedielectric substrate for the antenna, the coupling of the planar elementand the ground pattern becomes strong, and the adjustment of thedistance between them becomes necessary. Then, the shape of the sideedge portion of the planar element is formed as stated above, and thedistance between the planar element and the ground pattern is adjusted,so that the coupling degree is optimized, and the wide bandwidth can berealized.

Besides, a side of the ground pattern opposite to the dielectricsubstrate for the antenna may be constituted by a line segment. Thisindicates a case where the adjustment of the distance between the planarelement and the ground pattern is mainly performed by the shape of theplanar element.

Further, the ground pattern may have a tapered shape with respect to thedielectric substrate for the antenna, and the tapered shape may beconstituted by line segments. By adjusting the shape of the groundpattern as stated above, an antenna characteristic, especially animpedance characteristic, is improved.

Besides, the planar element may be symmetrical with respect to thestraight line passing through the feed position of the planar element.

Further, the dielectric substrate for the antenna may further include aresonant element connected to an end point of the planar element on thestraight line passing through the feed position. By providing theresonant element as stated above, a dual band antenna can be realized.

Besides, the resonant element may be symmetrical with respect to thestraight line passing through the feed position of the planar element.Besides, it may be asymmetrical.

Further, the planar element and the resonant element may be formed in asame layer of the dielectric substrate for the antenna.

Besides, the planar element and at least a part of the resonant elementmay be formed in different layers. By this structure, the dielectricsubstrate for the antenna can be miniaturized and the antenna can alsobe miniaturized as a whole.

Further, when the planar element and the resonant element are projectedon a virtual plane parallel to the layers in which the respectiveelements are formed, the resonant element may be disposed withoutoverlapping with a predetermined region defined beside the planarelement projected on the virtual plane. Besides, the resonant elementmay be disposed without overlapping with at least a region at a planarelement side with respect to a half line, which is parallel to thestraight line passing through the feed position of the planar elementprojected on the virtual plane and extends in a feed position directionfrom a start point that is an end point of the side edge portion of theprojected planar element and is a point remoter from the feed position.

By disposing the resonant element as stated above, the characteristicsof the planar element and the resonant element can be separatelycontrolled without exerting a bad influence on the characteristic of theplanar element.

A dielectric substrate for an antenna according to a second aspect ofthis invention comprises a dielectric layer, and a layer including aconductive planar element having a side edge portion constituted byeither one of a curved line and line segments, which are connected whiletheir inclinations are changed stepwise, and wherein a distance betweena side surface closest to a feed position of the planar element amongside surfaces of the dielectric substrate for the antenna and the sideedge portion is gradually increased to become saturated as being fartheraway from a straight line passing through the feed position.

By making the dielectric substrate for the antenna include the layer ofthe planar element, miniaturization of the antenna becomes possible.

Besides, the planar element may be symmetrical with respect to thestraight line passing through the feed position of the planar element.

Further, the second aspect of this invention may further include aresonant element connected to an end point of the planar element on thestraight line passing though the feed position of the planar element. Byproviding the resonant element as stated above, a dual band antenna canbe realized.

Besides, the resonant element may be symmetrical with respect to thestraight line passing through the feed position of the planar element.Besides, it may be asymmetrical.

Further, the planar element and the resonant element may be formed in asame layer of the dielectric substrate.

Besides, the planar element and at least a part of the resonant elementmay be formed in different layers of the dielectric substrate. By thisstructure, the dielectric substrate for the antenna can be miniaturized.

Further, when the planar element and the resonant element are projectedon a virtual plane parallel to the layers in which the respectiveelements are formed, the resonant element may be disposed withoutoverlapping with a predetermined region defined beside the planarelement projected on the virtual plane. Besides, the resonant elementmay be disposed without overlapping with at least a region at a planarelement side with respect to a half line, which is parallel to thestraight line passing through the feed position of the planar elementprojected on the virtual plane and extends in a feed position directionfrom a start point that is an end point of the side edge portion of theprojected planar element and is a point remoter from the feed position.

By disposing the resonant element as stated above, the characteristicsof the planar element and the resonant element can be separatelycontrolled without exerting a bad influence on the characteristic of theplanar element.

Incidentally, it can be said that the ground pattern and the planarelement or the dielectric substrate for the antenna are in anon-opposite state, and the respective planes are parallel orsubstantially parallel to each other. Besides, it can be said that theground pattern and the planar element or the dielectric substrate forthe antenna do not completely overlap with each other, and therespective planes are parallel or substantially parallel to each other.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a front view showing the structure of an antenna in a firstembodiment of this invention, and FIG. 1B is a side view thereof;

FIG. 2 is a diagram showing the structure of an antenna in a secondembodiment of this invention;

FIG. 3 is a diagram showing the structure of an antenna of a thirdembodiment of this invention;

FIG. 4 is a diagram showing the structure of an antenna of a fourthembodiment of the invention;

FIG. 5 is a diagram for explaining a region where a second elementexerts an influence on a first element;

FIG. 6A is a front view showing a mounting example in the fourthembodiment of this invention, and FIG. 6B is a bottom view thereof;

FIG. 7 is a diagram showing an impedance characteristic of a 2.4 GHzband in the fourth embodiment of this invention;

FIG. 8 is a diagram showing an impedance characteristic of a 5 GHz bandin the fourth embodiment of this invention;

FIGS. 9A, 9B and 9C are diagrams showing radiation patterns with respectto the electric wave of 2.45 GHz, and FIGS. 9D, 9E and 9F are diagramsshowing radiation patterns with respect to the electric wave of 5.4 GHzin the fourth embodiment of this invention;

FIG. 10 is a diagram showing a gain characteristic in the fourthembodiment of this invention;

FIGS. 11A, 11B and 11C are diagrams showing a layer structural exampleof a dielectric substrate for an antenna according to a fifth embodimentof this invention;

FIG. 12 is a diagram showing an impedance characteristic of a 5 GHz bandin the fifth embodiment of this invention;

FIG. 13 is a diagram showing an impedance characteristic of a 2.4 GHzband in the fifth embodiment of this invention;

FIGS. 14A, 14B and 14C are diagrams showing a layer structural exampleof a dielectric substrate for an antenna according to a sixth embodimentof this invention;

FIGS. 15A, 15B and 15C are diagrams showing a layer structural exampleof a dielectric substrate for an antenna according to a seventhembodiment of this invention;

FIGS. 16A, 16B and 16C are diagrams showing structures of conventionalantennas; and

FIG. 17 is a diagram showing a structure of a conventional antenna.

DETAILE DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments according to the present invention will bedescribed with reference to the accompanying drawings.

1. First Embodiment

FIGS. 1A and 1B show the structure of an antenna of a first embodimentof this invention. As shown in FIG. 1A, the antenna of this embodimentis constituted by a dielectric substrate 5 including a planar element 1in the inside thereof and having a dielectric constant of about 20, aground pattern 2 juxtaposed with the dielectric substrate 5, a substrate6, for example, a printed circuit board (more specifically, a resinsubstrate made of FR-4, Teflon (registered trademark) or the like), anda high frequency power source 3 connected to a feed point 1 a of theplanar element 1. The planar element 1 has a shape similar to a T shape,and is constituted by a bottom side 1 b along an end portion of thedielectric substrate 5, sides 1 c extending upward, sides 1 d having afirst inclination angle from the sides 1 c, sides 1 e having aninclination angle larger than the first inclination angle from the sides1 c, and a top portion 1 f. The feed point 1 a is provided at the middlepoint of the bottom side 1 b along the end portion of the dielectricsubstrate 5. In this embodiment, a distance L1 between the dielectricsubstrate 5 and the ground pattern 2 is 1.5 mm. Besides, the width ofthe ground pattern 2 is 20 mm.

Besides, the planar element 1 and the ground pattern 2 are symmetricalwith respect to a straight line 4 passing through the feed point 1 a.Besides, a length (hereinafter referred to as a distance) of a linesegment extending from a point on the sides 1 c, 1 d and 1 e of theplanar element 1 to the ground pattern 2 in parallel to the straightline 4 is symmetrical with respect to the straight line 4. That is, whenintervals between the points on the sides and the straight line 4 areidentical, the distances become identical.

In this embodiment, a side 2 a of the ground pattern 2 facing thedielectric substrate 5 is a straight line. Accordingly, the distance isgradually increased as an arbitrary point on the sides 1 c, 1 d and 1 emoves on the sides 1 c, 1 d and 1 e. That is, as the arbitrary pointmoves away from the straight line 4, the distance is increased.

Although a polygonal line constituted by connecting the sides 1 c, 1 dand 1 e is not a curved line, the inclination of each side is changedstepwise so that the distance is increased to become saturated. In otherwords, when the point moves away from the straight line 4 along thepolygonal line, although the distance is rapidly increased at first, theincrease rate is gradually decreased. That is, the shape is such thatshaving is performed inward from a straight line connecting an end pointof the top portion 1 f and an end point of the bottom side 1 b, whichare positioned at the same side when viewed from the straight line 4.

In this embodiment, the side edge portion of the planar element 1opposite to the side 2 a of the ground pattern 2 is constituted by thethree line segments 1 c, 1 d and 1 e. However, as long as the conditionthat the distance is increased to become saturated is satisfied, theshape of the side edge portion is not limited to this. Instead of thesides 1 c, 1 d and 1 e, a polygonal line constituted by an arbitrarynumber of line segments not less than two may be adopted. Besides,instead of the sides 1 c, 1 d and 1 e, the side edge portion may be acurved line convex upwardly with respect to the straight line connectingthe end point of the top portion 1 f and the end point of the bottomside 1 b, which are positioned at the same side when viewed from thestraight line 4. That is, when viewed from the planar element 1, thecurved line is convex inwardly.

Even when any shape is adopted, as the point moves away from thestraight line 4 along the sides 1 c, 1 d and 1 e, the distance iscontinuously changed, and by the existence of the continuous changingportion, a continuous resonance characteristic can be obtained at thelower limit frequency or higher. Incidentally, the lower limit frequencyis adjusted by changing the height of the planar element 1. However, itcan also be controlled by the length of the top portion 1 f, and/or theshape and length of the side edge portions with the reverse arc shape.

FIG. 1B is a side view in which the ground pattern 2 and the dielectricsubstrate 5 are provided on the substrate 6. There is also a case wherethe substrate 6 and the ground pattern 2 are integrally formed.Incidentally, in this embodiment, the planar element 1 is formed in theinside of the dielectric substrate 5. That is, the dielectric substrate5 is formed by laminating ceramic sheets, and the conductive planarelement 1 is also formed as one layer of them. Accordingly, actually,even if viewed from the above, it cannot be viewed as in FIG. 1A. Whenthe planar element 1 is constructed in the inside of the dielectricsubstrate 5, as compared with a case of exposure, an effect of thedielectric is slightly enhanced, and therefore, the miniaturization canbe achieved, and the reliability and/or resistance against rust or thelike is also increased. However, the planar element 1 may be formed onthe surface of the dielectric substrate 5. Besides, the dielectricconstant can also be changed, and either of a single layer substrate anda multilayer substrate may be used. In the case of the single layersubstrate, the planar element 1 is formed on the dielectric substrate 5.Incidentally, in this embodiment, the plane of the dielectric substrate5 is disposed parallel to or substantially parallel to the plane of theground pattern 2. By this arrangement, the plane of the planar element 1included in the one layer of the dielectric substrate 5 also becomesparallel to or substantially parallel to the plane of the ground pattern2.

As stated above, when the planar element 1 is formed so as to be coveredwith the dielectric substrate 5, the state of an electromagnetic fieldaround the planar element 1 is changed by the dielectric. Specifically,since an effect of increasing the density of the electric field in thedielectric and a wavelength shortening effect can be obtained, theplanar element 1 can be miniaturized. Besides, by these effects, alift-off angle of a current path is changed, and an inductance componentL and a capacitance component C in an impedance equivalent circuit ofthe antenna are changed. That is, a great influence occurs on theimpedance characteristic. When the shape is optimized so as to obtain adesired impedance characteristic in the bandwidth from 4.9 GHz to 5.8GHz in consideration of the influence on this impedance characteristic,the shape as shown in FIG. 1A has been obtained. This bandwidth is verywide as compared with the prior art.

Incidentally, it is conceivable that the planar element 1 is a radiationconductor of a monopole antenna similarly to the prior art. On the otherhand, it can be said that the antenna of this embodiment is a dipoleantenna since the ground pattern 2 also contributes to radiation.However, since the dipole antenna normally uses two radiation conductorshaving the same shape, the antenna of this embodiment can also be saidan asymmetrical dipole antenna. Further, the antenna of this embodimentcan also be said a traveling-wave antenna. The point of view as statedabove can be applied to all embodiments described below.

2. Embodiment 2

FIG. 2 shows a structure of an antenna of a second embodiment of thisinvention. As shown in FIG. 2, the antenna of this embodiment isconstituted by a dielectric substrate 15 including a planar element 11in the inside thereof and having a dielectric constant of about 20, aground pattern 12 juxtaposed with the dielectric substrate 15, asubstrate 16, for example, a printed circuit board, and a high frequencypower source 13 connected to a feed point 11 a of the planar element 11.The planar element 11 and the dielectric substrate 15 are the same asthe planar element 1 and the dielectric substrate 5 of the firstembodiment. In this embodiment, a distance L2 between the dielectricsubstrate 15 and the ground pattern 12 is 1.5 mm. Besides, the width ofthe ground pattern 12 is 20 mm.

Besides, the planar element 11 and the ground pattern 12 are symmetricalwith respect to a straight line 14 passing through the feed point 11 a.Besides, a length (hereinafter referred to as a distance) of a linesegment extending from a point on sides 11 c, 11 d and 11 e of theplanar element 11 to the ground pattern 12 in parallel to the straightline 14 is also symmetrical with respect to the straight line 14. Thatis, when intervals between the points on the sides 11 c, 11 d and 11 eand the straight line 14 are identical, the distances become identical.

In this embodiment, sides 12 a and 12 b of the ground pattern 12 facingthe dielectric substrate 15 are inclined so that as the point moves awayfrom the straight line 14 along the sides 11 c, 11 d and 11 e, thedistance between the planar element 11 and the ground pattern 12 becomeslong. In this embodiment, the height at the side edge portion of theground pattern 12 is lower than the height of a cross point of theground pattern and the straight line 14 by a length L3 (=2 to 3 mm).That is, the ground pattern 12 has a tapered shape formed of the upperedge portions 12 a and 12 b with respect to the dielectric substrate 15.The structure of the side surface is similar to FIG. 1B.

It is confirmed that when the sides 12 a and 12 b of the ground pattern12 are inclined as in this embodiment, in the bandwidth from 4.9 GHz to5.8 GHz, the impedance characteristic is better than the antenna of thefirst embodiment.

3. Embodiment 3

An antenna of a third embodiment of this invention is a dual bandantenna for a 2.4 GHz band and a 5 GHz band. As shown in FIG. 3, thedual band antenna is constituted by a dielectric substrate 25 includingin the inside thereof a planar first element 21 and a second element 27as a resonant element extending from a center of a top of the firstelement 21, a ground pattern 22 juxtaposed with the dielectric substrate25, disposed therefrom by an interval L5 (=1.5 mm) and having an upperedge portion of a tapered shape with respect to the dielectric substrate25, a substrate 26 on which the dielectric substrate 25 and the groundpattern 22 are placed, and a high frequency power source 23 connected toa feed point 21 a provided at the central portion of a bottom of thefirst element 21. The size of the dielectric substrate 25 is, forexample, 8 mm×4.5 mm×1 mm. Incidentally, the ground pattern 22 may beformed inside the substrate 26.

The first element 21 has a shape similar to a T shape, and specifically,has a shape similar to the planar element 1 shown in FIG. 1A. Bandwidthcontrol of the 5 GHz band is performed by a height L4 of this firstelement 21. However, the bandwidth can also be controlled by the lengthof a side of a top portion and/or the shape and length of side edgeportions with a reverse arc shape.

The ground pattern 22 has a width of 20 mm, and the height at both sideedge portions of the ground pattern 22 is lower than the height of across point of the ground pattern 22 and a straight line 24 passingthrough the feed point 21 a by L6 (=2 to 3 mm). That is, the groundpattern 22 has a tapered shape formed of upper edge portions 22 a and 22b with respect to the dielectric substrate 25. The structure of the sidesurface is almost similar to FIG. 1B except for the portion of thesecond element 27. However, the second element 27 is provided in thesame layer as the first element 21.

The first element 21 and the ground pattern 22 are symmetrical withrespect to the straight line 24. Besides, a length (hereinafter referredto as a distance) of a line segment extending from a point on the sideedge portions of the first element 21 to the ground pattern 22 inparallel to the straight line 24 is also symmetrical with respect to thestraight line 24. Further, the distance is gradually increased as thepoint on the side edge portions of the first element 21 moves away fromthe straight line 24.

The impedance characteristic is controlled by the shapes of the firstelement 21 and the ground pattern 22 as stated above. Besides, theresonant frequency of the 2.4 GHz band is controlled by adjusting thelength of the second element 27 from a connected portion with the firstelement 21 to an open end. Incidentally, the second element 27 has abent shape so that miniaturization is achieved without exerting a badinfluence on the characteristic of the first element 21.

By adopting the shapes as stated above, the electric characteristics ofthe 5 GHz band and the 2.4 GHz band can be separately controlled. The 5GHz band and the 2.4 GHz band are ranges used in the standard ofwireless LAN (Local Area Network), and this embodiment capable ofsupporting both the frequency ranges is very useful.

4. Embodiment 4

An antenna of a fourth embodiment of this invention is a dual bandantenna for a 2.4 GHz band and a 5 GHz band. The dual band antenna isconstituted by, as shown in FIG. 4, a dielectric substrate 35 includingin the inside thereof a planar first element 31 and a second element 37as a resonant element extending from a center of a top of the firstelement 31, a ground pattern 32 juxtaposed with the dielectric substrate35, disposed therefrom by an interval L8 (=1.5 mm) and having an upperedge portion of a tapered shape with respect to the dielectric substrate35, a substrate 36 on which the dielectric substrate 35 and the groundpattern 32 are placed, and a high frequency power source 33 connected toa feed point 31 a provided at the central portion of a bottom of thefirst element 31. The size of the dielectric substrate 35 is, forexample, 10 mm×5 mm×1 mm.

The first element 31 has a shape similar to a T shape, and morespecifically has a shape similar to the planar element 1 shown in FIG.1A. The bandwidth control of the 5 GHz band is performed by a height L7of the first element 31. However, it can also be controlled by thelength of a side of a top portion, and/or the shape and length of sideedge portions with a reverse arc shape.

The ground pattern 32 has a width of 20 mm, and the height of the sideedge portions of the ground pattern 32 are lower than the height of across point of the ground pattern and a straight line 34 passing throughthe feed point 31 a by L9 (=2 to 3 mm). That is, the ground pattern 32has a tapered shape formed of upper edge portions 32 a and 32 b withrespect to the dielectric substrate 35. The structure of the sidesurface is almost similar to FIG. 1B except for the portion of thesecond element 37. However, the second element 37 is provided in thesame layer as the first element 31.

The first element 31, the second element 37, and the ground pattern 32are symmetrical with respect to the straight line 34. Besides, a length(hereinafter referred to as a distance) of a line segment extending froma point on the side edge portion of the first element 31 to the groundpattern 32 in parallel to the straight line 34 is also symmetrical withrespect to the straight line 34. Further, the distance is graduallyincreased as the point on the side edge portions of the first element 31moves away from the straight line 34.

The impedance characteristic is controlled by the shapes of the firstelement 31 and the ground pattern 32 as set forth above. The resonantfrequency of the 2.4 GHz band is controlled by adjusting the length ofthe second element 37 from a connected portion with the first element 31to an open end. Incidentally, a meander portion of the second element 37is formed at upper side of the dielectric substrate. This is forcarrying out an efficient arrangement in a limited space while a badinfluence is not exerted on the characteristic of the first element 31.As shown in FIG. 5, a space 38 is a portion where a bad influence isexerted on the characteristic of the first element 31, and the secondelement 37 is not disposed in this portion. Besides, the second element37 is not disposed in at least a region closer to the first element 31than a dotted line 38 a. This dotted line 38 a is a half line extendingin parallel to the straight line 34 toward the feed point 31 a from astart point that is an end point of the side edge portion of the firstelement 31 and is remoter from the feed point 31 a.

By adopting the shape as stated above, the electrical characteristics ofthe 5 GHz band and the 2.4 GHz band can be separately controlled. The 5GHz band and the 2.4 GHz band are ranges used in the standard ofwireless LAN, and this embodiment capable of supporting both thefrequency bands is very useful.

Antenna characteristics in a case where for example, an implementationform as shown in FIGS. 6A and 6B is adopted will be given. As shown inFIGS. 6A and 6B, the dielectric substrate 35 is juxtaposed with a groundpattern 39 whose upper edge portion is horizontal and is disposedtherefrom by an interval of 1.5 mm. As shown in FIG. 4, the size of thedielectric substrate 35 is 10 mm×5 mm×1 mm, and includes the firstelement 31 and the second element 37. On the other hand, as for the sizeof the ground pattern 39, the height is 47 mm and the width is 12 mm.The thickness of the substrate 36 is 0.8 mm. Incidentally, it is assumedthat the drawing shown in FIG. 6A is an XY plane, and the drawing shownin FIG. 6B is an XZ plane.

At this time, the impedance characteristic of the second element 37 isas shown in FIG. 7. In FIG. 7, the axis of ordinate indicates the VSWR,and the axis of abscissa indicates the frequency (GHz). The frequency atwhich the VSWR is smallest is about 2.45 GHz, and the frequencybandwidth in which the VSWR is 2 or less is from about 2.20 GHz to 2.67GHz, so that about 470 MHz is secured. On the other hand, the impedancecharacteristic of the first element 31 is as shown in FIG. 8. Thefrequency at which the VSWR is smallest is about 5.2 GHz, and thefrequency bandwidth in which the VSWR is 2 or less is about 4.6 GHz to 6GHz or more, so that at least 1.4 GHz is secured. As stated above, thewide bandwidth is realized for both the second element 37 and the firstelement 31. That is, it is indicated that the antenna of the embodimenthas a sufficient function as the dual band antenna. Incidentally, theground pattern 39 may be tapered toward the dielectric substrate 35.

Besides, the directivity of the antenna shown in FIGS. 6A and 6B will beshown in FIGS. 9A to 9F. FIG. 9A shows radiation patterns when electricwaves of 2.45 GHz are transmitted from a transmission side antenna, andthe reception side antenna shown in FIGS. 6A and 6B is rotated while ameasurement plane is set to the XY plane. Incidentally, with respect toconcentric circles, the center indicates −45 dBi, the outermost circleindicates 5 dBi, and an interval between the respective circles is 10dBi. Here, an inside solid line indicates the radiation pattern of thereception side antenna in the case where the electric wave of thevertical polarization is transmitted from the transmission side antenna,and an outside thick line indicates the radiation pattern of thereception side antenna in the case where the electric wave of thehorizontal polarization is transmitted from the transmission sideantenna. It is understood that the radiation pattern for thehorizontally polarized wave shows larger gain in all directions.Besides, in the case of the vertically polarized wave, it appears thatthere is directivity in directions of 0°, −90° and 180°. Incidentally,an upper right picture shows the antenna of FIGS. 6A and 6B. A blackenedportion is a position where the dielectric substrate 35 is placed. Avertical arrow indicates a direction of 0°, and an angle is increased ina direction of +θ.

Similarly, FIG. 9B shows radiation patterns when electric waves of 2.45GHz are transmitted from the transmission side antenna, and thereception side antenna shown in FIGS. 6A and 6B is rotated while the YZplane is set to a measurement plane. Similarly to the above, a solidline indicates the radiation pattern of the reception side antenna inthe case where the electric wave of the vertically polarization istransmitted from the transmission side antenna, and a thick lineindicates the radiation pattern of the reception side antenna in thecase where the electric wave of the horizontal polarization istransmitted from the transmission side antenna. It appears that theradiation pattern for the horizontally polarized wave has directivity indirections of 0° and 180°. Besides, it appears that the radiationpattern for the vertically polarized wave has directivity in directionsof 0°, 90° and 180°. Incidentally, the meaning of an upper right pictureis the same as in FIG. 9A.

FIG. 9C shows radiation patterns when electric waves of 2.45 GHz aretransmitted from the transmission side antenna, and the reception sideantenna shown in FIGS. 6A and 6B is rotated while the measurement planeis set to the XZ plane. Similarly to the above, a solid line indicatesthe radiation pattern of the reception side antenna in the case wherethe electric wave of the vertical polarization is transmitted from thetransmission side antenna, and a thick line indicates the radiationpattern of the reception side antenna in the case where the electricwave of the horizontal polarization is transmitted from the transmissionside antenna. It appears that the radiation pattern for the horizontallypolarized wave has directivity in directions of 0° and 180°. Besides,the radiation pattern for the vertically polarized wave hasnon-directivity. Incidentally, the meaning of an upper right picture isthe same as in FIG. 9A.

FIG. 9D shows radiation patterns when electric waves of 5.4 GHz aretransmitted from the transmission side antenna, and the reception sideantenna shown in FIGS. 6A and 6B is rotated while the measurement planeis set to the XY plane. Similarly to the above, a solid line indicatesthe radiation pattern of the reception side antenna in the case wherethe electric wave of the vertical polarization is transmitted from thetransmission side antenna, and a thick line indicates the radiationpattern of the reception side antenna in the case where the electricwave of the horizontal polarization is transmitted from the transmissionside antenna. It appears that the radiation pattern for the horizontallypolarized wave has directivity in directions of 45°, 135°, −45° and−135°. Besides, it appears that the radiation pattern for the verticallypolarized wave has non-directivity except for the direction of 90°.Incidentally, the meaning of an upper right picture is the same as inFIG. 9A.

FIG. 9E shows radiation patterns when electric waves of 5.4 GHz aretransmitted from the transmission side antenna, and the reception sideantenna shown in FIGS. 6A and 6B is rotated while the measurement planeis set to the YZ plane. Similarly to the above, a solid line indicatesthe radiation pattern of the reception side antenna in the case wherethe electric wave of the vertical polarization is transmitted from thetransmission side antenna, and a thick line indicates the radiationpattern of the reception side antenna in the case where the electricwave of the horizontal polarization is transmitted from the transmissionside antenna. It appears that the radiation pattern for the horizontallypolarized wave has directivity in directions of 45°, 135°, −45° and−135°. Besides, it appears that the radiation pattern for the verticallypolarized wave has directivity with a complicated shape. Incidentally,the meaning of an upper right picture is the same as in FIG. 9A.

FIG. 9F shows radiation patterns when electric waves of 5.4 GHz aretransmitted from the transmission side antenna, and the reception sideantenna shown in FIGS. 6A and 6B is rotated while the measurement planeis set to the XZ plane. Similarly to the above, a solid line indicatesthe radiation pattern of the reception side antenna in the case wherethe electric wave of the vertical polarization is transmitted from thetransmission side antenna, and a thick line indicates the radiationpattern of the reception side antenna in the case where the electricwave of the horizontal polarization is transmitted from the transmissionside antenna. It appears that the radiation pattern for the horizontallypolarized wave has directivity of a complicated shape. Besides, itappears that the radiation pattern for the vertically polarized wave hasnon-directivity except for the direction of −45°. Incidentally, themeaning of an upper right picture is the same as in FIG. 9A.

FIG. 10 collectively shows data of average gains. For each of theplanes, the average gain of 2.45 GHz and the average gain for 5.4 GHzwith respect to the vertically polarized wave (V) and the horizontallypolarized wave (H) are indicated. Further, the total average gains for2.45 GHz and 5.4 GHz are also indicated. From this, with respect to 2.45GHz, the gain for the vertically polarized wave on the XZ plane is high,and with respect to the horizontally polarized wave, the gain is high onthe YZ plane or the XY plane. Besides, with respect to 5.4 GHz, the gainfor the horizontally polarized wave on the YZ plane or the XY plane ishigh, and with respect to the vertically polarized wave, the gain isrelatively high on the XZ plane.

5. Embodiment 5

An antenna of a fifth embodiment of this invention is a dual bandantenna for a 2.4 GHz band and a 5 GHz band, and here, a contrivance tofurther miniaturize the dielectric substrate 35 of the fourth embodimentwill be described. The dual band antenna has a structure in which asshown in a side view of FIG. 11A, a planar first element 41 and a firstportion 47 a of a second element as a resonant element are formed in arelatively low layer of a dielectric substrate 46, second portions 47 bof the second element are formed in a relatively high layer of thedielectric substrate 46, and they are connected by two externalelectrodes 46 a. FIG. 11B shows a structure of the layer in which thefirst element 41 and the first portion 47 a of the second element areformed. The shape of the first element 41 is the same as that shown inthe fourth embodiment. The first portion 47 a of the second elementextends from the center of the top of the first element 41, branches outinto two directions halfway, and the branch portions are connected tothe two external electrodes 46 a provided at the upper end portion ofthe dielectric substrate 46. FIG. 11C shows a structure of the layer inwhich the second portions 47 b of the second element is formed. Thesecond portions 47 b of the second element have such structure thatafter they extend from the external electrode 46 a provided at the upperend portion of the dielectric substrate 46 in the direction toward thelower end portion of the dielectric substrate 46, they include themeander portions shown in the fourth embodiment (FIG. 4). The secondportions 47 b of the second element are disposed so as not to overlapwith the first element 41 when viewed from the above though they areprovided in the different layers. Similarly to the arrangement shown inFIG. 5 in the fourth embodiment, when viewed from the above, they aredisposed so as not to overlap with at least the region where a badinfluence is exerted on the first element 41. That is, when the secondportions 47 b of the second element and the first element 41 areprojected on a virtual plane parallel to the layers in which they areformed, the second portions 47 b of the second element are disposed notto overlap with predetermined regions defined beside the first elementprojected on the virtual plane. The predetermined regions are portionscorresponding to the regions 38 shown in FIG. 5. Incidentally, as forthe size of the dielectric substrate 46 in this embodiment, L10=1 mm,L11=4 mm, and L12=10 mm.

The resonant frequency of the second element is controlled by adjustingthe length of the second element from a connected portion with the firstelement 41 to the open ends. When compared with the fourth embodiment,the portions, as the first portions 47 a of the second element,extending toward the external electrodes 46 a, the portions of theexternal electrodes 46 a, and the portions, as the second portions 47 bof the second element, vertically extending from the external electrodes46 a are added as the length of the second element. Thus, even if thesecond portions 47 b of the second element are shortened, thecharacteristic of the 2.4 GHz band can be kept at the same level as theantenna of the fourth embodiment. By this structure, miniaturization ofthe dielectric substrate 46 can be realized.

FIG. 12 shows the impedance characteristic of the 5 GHz band in thisembodiment. In FIG. 12, the axis of ordinate indicates the VSWR, and theaxis of abscissa indicates the frequency (GHz). When compared with FIG.8 showing the impedance characteristic of the 5 GHz band according tothe fourth embodiment, although the shape of the curved line is slightlydifferent, the bandwidth in which the VSWR is 2 or less is almostidentical.

FIG. 13 shows the impedance characteristic of the 2.4 GHz band in thisembodiment. In FIG. 13, the axis of ordinate indicates the VSWR, and theaxis of abscissa indicates the frequency (GHz). When compared with FIG.7 showing the impedance characteristic of the 2.4 GHz band according tothe fourth embodiment, the bandwidth in which the VSWR is 2 or less, inFIG. 13 showing the miniaturized case becomes wider at the highfrequency side by about 80 MHz. Thus, it is understood that theexcellent characteristic is represented as stated above.

6. Embodiment 6

An antenna of a sixth embodiment of this invention is a dual bandantenna for a 2.4 GHz band and a 5 GHz band, and here, a contrivance tofurther miniaturize the dielectric substrate 35 of the fourth embodimentwill be described. The dual band antenna has a structure in which asshown in a side view of FIG. 14A, a planar first element 51 and a firstportion 57 a of a second element as a resonant element are formed in arelatively low layer of a dielectric substrate 56, a second portion 57 bof the second element is formed in a relatively high layer of thedielectric substrate 56, and they are connected to each other by oneexternal electrode 56 a. FIG. 14B shows a structure of the layer inwhich the first element 51 and the first portion 57 a of the secondelement are formed. The shape of the first element 51 is the same asthat shown in the fourth embodiment. The first portion 57 a of thesecond element extends from the center of the top of the first element51, and is linearly connected to the external electrode 56 a provided atthe upper end portion of the dielectric substrate 56. FIG. 14C shows astructure of the layer in which the second portion 57 b of the secondelement is formed. The second portion 57 b of the second element hassuch a structure that after it extends from the external electrode 56 aprovided at the upper end portion of the dielectric substrate 56 in thedirection toward the lower end portion of the dielectric substrate 56,it includes most of the second element 37 shown in the fourth embodiment(FIG. 4) except for the portion for connection to the first element 31.The second portion 57 b of the second element is disposed so as not tooverlap with the first element 51 when viewed from the above though theyare provided in the different layers. Similarly to the arrangement shownin FIG. 5 in the fourth embodiment, when viewed from the above, it isdisposed so as not to overlap with at least the region where a badinfluence is exerted on the first element 51.

The resonant frequency of the second element is controlled by adjustingthe length of the second element from a connected portion with the firstelement 51 to the open ends. When compared with the fourth embodiment,the portion, as the first portion 57 a of the second element, extendingtoward the external electrode 56 a, the portion of the externalelectrode 56 a, and the portion, as the second portion 57 b of thesecond element, vertically extending from the external electrode 56 aare added as the length of the second element. Thus, even if the secondportion 57 b of the second element is shortened, the characteristic ofthe 2.4 GHz band can be kept at the same level as the antenna of thefourth embodiment. By this structure, miniaturization of the dielectricsubstrate 56 can be realized.

7. Embodiment 7

An antenna of a seventh embodiment of this invention is a dual bandantenna for a 2.4 GHz band and a 5 GHz band, and here, a contrivance tofurther miniaturize the dielectric substrate 35 of the fourth embodimentwill be described. The dual band antenna has a structure in which asshown in a side view of FIG. 15A, a planar first element 61 and a firstportion 67 a of a second element as a resonant element are formed in arelatively low layer of a dielectric substrate 66, second portions 67 bof the second element are formed in a relatively high layer of thedielectric substrate 66, and they are connected via two externalelectrodes 66 a. FIG. 15B shows a structure of the layer in which thefirst element 61 and the first portion 67 a of the second element areformed. The shape of the first element 61 is the same as that shown inthe fourth embodiment. The first portion 67 a of the second elementextends from the center of the top of the first element 61, branches outinto two directions halfway, and the branch portions extend beyond theside width of the first element 61, and then, they are connected to thetwo external electrodes 66 a provided at the upper end portion of thedielectric substrate 66. FIG. 15C shows a structure of the layer inwhich the second portions 67 b of the second element are formed. Thesecond portions 67 b of the second element have such structure thatafter they extend from the external electrodes 66 a provided at theupper end portion of the dielectric substrate 66 in the direction towardthe lower end portion of the dielectric substrate 66, they include themeander portions. The second portions 67 b of the second element aredisposed so as not to overlap with the first element 61 when viewed fromthe above though they are provided in the different layers. Similarly tothe arrangement shown in FIG. 5 in the fourth embodiment, when viewedfrom the above, they are disposed so as not to overlap with at least theregions where a bad influence is exerted on the first element 61.

The resonant frequency of the second element is controlled by adjustingthe length of the second element from a connected portion with the firstelement 61 to the open ends. When compared with the fourth embodiment,the portions, as the first portion 67 a of the second element, extendingtoward the external electrodes 66 a, the portions of the externalelectrodes 66 a, and the portions, as the second portions 67 b of thesecond element, vertically extending from the external electrodes 66 aare added as the length of the second element. Thus, even if the secondportions 67 b of the second element are shortened, the characteristic ofthe 2.4 GHz band can be kept at the same level as the antenna of thefourth embodiment. By this structure, miniaturization of the dielectricsubstrate 66 can be realized.

Although the embodiments of the invention have been described, theinvention is not limited to these. For example, as the shape of theplanar element and the resonant element, a different shape can beadopted as long as a similar antenna characteristic can be obtained.Besides, as the tapered shape of the ground pattern, although theexample in which the upper edge portion is the straight line has beendescribed, a curved line convex upwardly or downwardly may be adopted.Besides, there is also a case where a recess for accommodating anelectrode for feeding is provided in the upper edge portion of theground pattern. Further, an implementation example is not limited tothat shown in FIG. 6. That is, implementation can also be performed on awireless communication card, such as a PC card or a compact flash(registered trademark) (CF) card, which is inserted in a slot of apersonal computer or a PDA (Personal Digital Assistant) and is used. Foradjustment of the antenna characteristic at the time of theimplementation, the ground pattern may be extended up to the right orthe left of the dielectric substrate. Besides, two dielectric substratesmay be provided on upper end portions of a substrate so that they do notinterfere with each other, and a space diversity antenna may bestructured. Further, the dielectric substrate can be mounted on a smallstick type card.

Although the present invention has been described with respect to aspecific preferred embodiment thereof, various change and modificationsmay be suggested to one skilled in the art, and it is intended that thepresent invention encompass such changes and modifications as fallwithin the scope of the appended claims.

1. An antenna, comprising: a planar element that is fed at a feedposition; and a ground pattern that is juxtaposed with said planarelement, and wherein a distance between said planar element and saidground pattern is gradually increased so that the increase of saiddistance becomes saturated as being farther away from a straight linepassing through said feed position, said antenna further comprises aresonant element connected to an end point of said planar element onsaid straight line passing through said feed position of said planarelement, said planar element and said resonant element are symmetricalwith respect to said straight line passing through said feed position ofsaid planar element, and said planar element and said resonant elementare formed on or inside a dielectric substrate.
 2. The antenna as setforth in claim 1, wherein a side edge portion of said planar element isconstituted by either one of a curved line and a plurality of linesegments, which are connected while their inclinations are changedstepwise.
 3. The antenna as set forth in claim 1, wherein said planarelement and said resonant element is formed in a same layer of saiddielectric substrate.
 4. The antenna as set forth in claim 1, whereinsaid planar element and at least a part of said resonant element isformed in different layers.
 5. The antenna as set forth in claim 1,wherein when said planar element and said resonant element are projectedon a virtual plane parallel to layers in which the respective elementsare formed, said resonant element is disposed without overlapping with apredetermined region defined beside said planar element projected onsaid virtual plane.
 6. The antenna as set forth in claim 1 wherein whensaid planar element and said resonant element are projected on a virtualplane parallel to layers in which the respective elements are formed,said resonant element is disposed without overlapping with at least aregion at a planar element side with respect to a half line, which isparallel to said straight line passing through said feed position of theprojected planar element and extends in a feed position direction from astart point that is an end point of said side edge portion of theprojected planar element and is a point remoter from said feed position.7. A dielectric substrate for an antenna, comprising: a dielectriclayer; and a layer including a conductive planar element having a sideedge portion constituted by either one of a curved line and linesegments, which are connected while their inclinations are changedstepwise, and wherein a distance between a side surface closest to afeed position of said planar element among side surfaces of saiddielectric substrate and said side edge portion is gradually increasedso that the increase of said distance becomes saturated as being fartheraway from a straight line passing through said feed position, saiddielectric substrate further comprises a resonant element connected toan end point of said planar element on said straight line passingthrough said feed position of said planar element, and said resonantelement is symmetrical with respect to said straight line passingthrough said feed position of said planar element.
 8. The dielectricsubstrate as set forth in claim 7, wherein said planar element and saidresonant element are formed in a same layer of said dielectricsubstrate.
 9. The dielectric substrate as set forth in claim 7, whereinsaid planar element and at least a part of said resonant element areformed in different layers of said dielectric substrate.
 10. Thedielectric substrate as set forth in claim 7, wherein when said planarelement and said resonant element are projected on a virtual planeparallel to layers in which the respective elements are formed, saidresonant element is disposed without overlapping with a predeterminedregion defined beside said planar element projected on said virtualplane.
 11. The dielectric substrate as set forth in claim 7, whereinwhen said planar element and said resonant element are projected on avirtual plane parallel to layers in which the respective elements areformed, said resonant element is disposed without overlapping with atleast a region at a planar element side with respect to a half line,which is parallel to said straight line passing through said feedposition of the projected planar element and extends in a feed positiondirection from a start point that is an end point of said side edgeportion of the projected planar element and is a point remoter from saidfeed position.
 12. An antenna comprising: a planar element that is fedat a feed position; a ground pattern that is juxtaposed with said planarelement; and a second element that is connected with said planarelement, wherein said second element is connected with a first edge partof said planar element, said first edge part being opposite to a secondedge part of said planar element, said second edge part being adjacentto said ground pattern, and said planar element and said second elementare symmetrical with respect to said straight line passing through saidfeed position of said planar element.